2D means 'two dimensional'. 2D barcodes contain more information than conventional one dimensional linear barcodes. Conventional barcodes get wider as more data is encoded. 2D barcodes make use of the vertical dimension to pack in more data. Two dimensional codes have been classified by their relative geometry. A 2D (two-dimensional) barcode is a graphical image that stores information both horizontally -- as one-dimensional bar codes do -- and vertically.

The two most popular types are covered here: Stacked codes and matrix codes. Stacked codes are made up of two or more rows of bars and spaces that are “stacked” on each other – sometimes referred to as “stacked linear”. Examples of stacked codes are Code 49, Code 16K and PDF417. Matrix codes encode information using fixed-width light and dark cells. Some experts consider matrix codes to be “true” 2D codes. Example of matrix codes include Data Matrix, MaxiCode, Aztec Code, QR Code and Code One.

Two dimensional symbols can be used on labels with limited space, less than .75 inches (1.9 cm) square, and when there is the need to capture a small amount of data, less than 50 characters. In this application, a scalable matrix code such as Data Matrix, Aztec Code, QR Code, or Code One works best because a matrix code offers much higher density than 2D stacked codes such as PDF417, which are designed to encode large amounts of data. Code 49 or Code 16K should also be considered to address small space requirements if you need to encode a more limited number of characters. MicroPDF417, new stacked symbology which is undergoing standardization, could also be considered for small space applications in which the symbol data capacity required is limited to 250 alphanumeric characters or 3 digits. An example of an application requiring small labels is to track manufacturer, item code, and traceability code on an electronic component.

Two Dimensional bar codes have been developed, placed in the public domain and published as AIM standards since 1987. These codes can be classified into two groups: stacked codes, sometimes referred to as “stacked linear”, and matrix codes. Code 49 was the first 2D stacked bar code invented by Intermec in 1987, followed by Code 16K developed by Laserlight Systems in 1988. PDF417, developed by Symbol Technologies in 1992, is also a stacked code, but it can accommodate a much higher data capacity (over 1800 characters) in comparison to Code 49 or Code 16 K, which can encode around 50 characters given reasonable symbol density.

Matrix codes also can hold large amounts of data, but within a much smaller size. These codes, such as Data Matrix, MaxiCode, Aztec Code, QR Code, and Code One, require reading by a 2D imaging device. Reduced Quiet Zones for matrix codes (except for Aztec Code and Code One in which none is required) allow symbol location in much closer proximity to surrounding text and/or graphics. Each 2D matrix code has a unique “finder pattern” or recognition pattern that reference the symbol type for the scanner.

MaxiCode has three concentric circles or a “bulls-eye” pattern; Data Matrix uses an “L” pattern bordering the left and bottom edge, Aztec Code uses a square bulls-eye; QR Code uses three square patterns the corners of the code; and Code One uses a series of horizontal lines (from three to six depending on the version) and from two to fourteen vertical recognition patterns.

2D barcodes are also known as quick response codes because they enable fast data access. 2D barcodes are often used in conjunction with smart phones. Japan is already QR-crazy. Google wants the U.S. to be next. Google has mailed out window stickers with two-dimensional bar codes (aka, QR codes ) to the most-searched for or clicked-on businesses in its local business directory. Anyone with a QR code reader in their phone can scan it to call up a Google Mobile local directory page for one of these “Favorite Places” which generally includes a map, phone number, directions, address, reviews, and a link to the store’s website. (It’s a mobile version of Google Place).